Is this the same Lost Lake Road in Groton? I remember I wanted to do a smoother metric last year so I drove over to ride and chose a route starting in Lancaster, went through Shirley, Townsend, Groton, and Ayer. I was on rt 40 in Groton and decided to cross south over on a road called Lost Lake Rd to pop in and say a quick hi to friends on the other side. It was funny. You go down the road and you sort of get enveloped in this lost world of green and like you say, continually go over all these roller coaster hills - it sort of makes you laugh. Short stand in the pedals sprinty kind of hills but I do remember rolling my eyes saying "how many are there" and I do remember one that was over 10%.
Indeed, this is the one. It's very close to our house and I've never ridden it before, mainly due to the cars that are having fun driving the road too. But it wasn't too bad.